Arthritis & Rheumatism, Volume 63,
November 2011 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Chicago, Illinois November 4-9, 2011.

Epidemiology of Idiopathic Inflammatory Myopathy in a Large United States Managed Care Population.

Furst1,  Daniel E., Amato2,  Anthony A., Iorga3,  Serban R., Gajria4,  Kavita, Fernandes4,  Ancilla

UCLA Medical School, Los Angeles, CA
Brigham and Women's Hospital and Harvard Medical School, Boston, MA
Innovus, Eden Prairie, MN
MedImmune LLC, Gaithersburg, MD


Prior studies have reported low incidence (0.1–1 per 100,000 persons) and prevalence (0.55–6 per 100,000 persons) of idiopathic inflammatory myopathies (IIMs) in the United States. However, updated estimates on the incidence and prevalence of IIMs have not been easily available.


We conducted a retrospective study of IIMs in a large US managed care database. Subjects were included in the incidence cohort if they had a medical claim with a myositis diagnosis (ICD-9-CM 710.3 [dermatomyositis/DM], 710.4 [polymyositis/PM], 728.81 [interstitial myositis]) and an index date from 2003–2008 that satisfied the following: 1) at least 1 inpatient claim or >=2 office or ER visits at least 30 days apart with a diagnosis code for myositis; 2) >=18 years of age on the index date; 3) continuously enrolled for 12 months before and after the index date; and 4) no myositis claims 12 months prior to index date. Subjects were identified for the prevalence cohort using the same criteria, with the exception of requirement 4. Overall and annual incidence for the duration of 2003–2008 was estimated and age-gender adjusted to the US 2000 census population. Annual prevalence was calculated for each year from 2003 to 2008. Subjects contributed to annual incidence once (the earliest service date that met the above criteria was set as the index date), but could contribute to prevalence in multiple years. Sensitivity analyses were performed using select clinical characteristics (presence of muscle biopsy or rheumatologist/neurologist/dermatologist visit) and treatments (presence of medications used to treat IIMs).


A total of 1941 subjects were included in the incidence cohort (65% female, median age=49). For the duration of 2003–2008, the overall adjusted incidence rate for myositis was 6.57 cases (95% CI, 6.20–6.94) per 100,000 person-years. Similarly, the overall adjusted rates for PM, DM, and interstitial myositis were 3.79, 1.38, and 1.69 per 100,000 person-years, respectively. The adjusted annual incidence of myositis ranged from 5.81 to 7.89 per 100,000 persons from 2003 to 2008. From sensitivity analyses (using clinical/treatment characteristics), the overall adjusted incidence rate was 5.07 cases per 100,000 person-years (95% CI, 4.73–5.40). A total of 3112 subjects were included in the prevalence cohort (67% female, median age=49). The annual prevalence of myositis ranged from 13.99 in 2003 to 17.37 in 2008 per 100,000 persons. In sensitivity analyses (using clinical characteristics), the annual prevalence decreased slightly to range between 9.59 in 2003 to 13.61 in 2008 per 100,000 persons.


Our findings suggest that the incidence and prevalence of IIMs in the managed care database are higher than those previously reported. Due to the limitations inherent in claims analysis, such as plan turnover, additional research is needed to substantiate these results. Understanding the epidemiology of these rare conditions may help increase the awareness of healthcare providers and eventually contribute to early diagnosis and treatment of these debilitating conditions.

To cite this abstract, please use the following information:
Furst, Daniel E., Amato, Anthony A., Iorga, Serban R., Gajria, Kavita, Fernandes, Ancilla; Epidemiology of Idiopathic Inflammatory Myopathy in a Large United States Managed Care Population. [abstract]. Arthritis Rheum 2011;63 Suppl 10 :1864

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